Next to or below the login details, you will find a button called "Grids" in Hippo, "Edit Saved Logins" in Phoenix and "Grid Manager" in Imprudence. The name and exact position of the button varies between viewers.
Click on "add" in the left pane, enter oceangrid or similar as the grid name, http://oceangrid.net/ as the Login URI, then hit the button "Get Grid Info". This should automatically fill the other fields. You can enter them manually if not. Hit "Ok" and choose "oceangrid" in the drop-down menu.
Now you are good to go.
You can also check out the list of third-party viewers for more options.